1. Field of the Invention
The present invention relates to a paper feeder comprising a sheet tray provided along a guide portion mounted on a main body of an image forming apparatus and capable of being pushed in and pulled out in horizontal directions with respect to the main body; a bottom plate provided inside the sheet tray to be vertically movable; an elevating device for raising the bottom plate as the sheet tray is pushed into the main body and lowering the bottom plate as the sheet tray is pulled out of the main body; the main body having an actuator capable of contacting an upper surface of a sheet placed on the bottom plate as the bottom plate is raised, and a sensor capable of detecting the sheet on the sheet tray based on the actuator contacting the upper surface of the sheet; and a through bore or a recess formed in the bottom plate for receiving the actuator when the sheet tray is empty of a sheet, for enabling the sensor to detect that the sheet tray is empty of a sheet.
2. Description of the Related Art
With the paper feeder noted above, the bottom plate mounted inside the sheet tray is raised when the sheet tray is pushed into the main body of the image forming apparatus, to move an uppermost one of the sheets stacked on the bottom plate to a predetermined vertical position for feeding, and the actuator mounted on the main body contacts the upper surface of the sheets placed on the bottom plate whereby the sensor detects that the sheets are present. The through bore or recess is formed in the bottom plate for receiving the actuator when sheets are absent in order to prevent the sensor from erroneously detecting that sheets are present due to contact between the actuator and the bottom plate. As the actuator moves into the through bore or recess, the sensor detects that the sheets are absent.
When the sheet tray is forced out of the main body in a state where the sensor detects that sheets are absent with the actuator lying in the through bore or recess, the actuator will collide with peripheries of the bottom plate surrounding the through bore or recess due to the pull-out operation, which can cause damage. In view of this, the elevating device is provided to raise the bottom plate as the sheet tray is pushed into the main body, and to lower the bottom plate as the sheet tray is pulled out of the main body.
However, when the sheet tray is pulled out at a speed faster than a descending speed of the bottom plate, i.e., when the sheet tray is forcibly pulled out before the bottom plate descends sufficiently or before the actuator of the main body moves out of the through bore or recess, the actuator may collide with the peripheries of the bottom plate due to the pull-out operation, and can be damaged.
In view of the above, the conventional paper feeder controls the operation of the elevating device so that the bottom plate descends to a predetermined vertical position where the actuator moves out of the through bore or recess as the sensor detects that sheets are absent thereby preventing the actuator from colliding with the peripheries of the bottom plate when the sheet tray is pulled out of the main body (see Japanese laid-open Publication No. 2002-284367, for example).
This disadvantageously complicates the controlling structure of the elevating device. In addition, if the sheet tray is forcibly pulled out of the main body immediately after the sensor detects that the sheets are absent and before the actuator is completely out of the through bore or recess, there still remains the possibility that the actuator is damaged by collision with the peripheries of the bottom plate.